Today's wireless telecommunications networks provide telephone subscribers with the ability to access telecommunications services from almost anywhere in the world. One of the keys to facilitating such world-wide access is mobility management. With mobility management, wireless networks are able to track the locations of mobile devices so that mobile services can be delivered to the mobile devices.
A wireless network is typically formed of a number of cells, each covering a small geographic area within which a mobile device, such as a laptop or smartphone, may receive mobile services. A cell is typically equipped with a base station that provides radio coverage to the cell, thereby enabling communication with mobile devices located within the cell. By integrating the coverage of multiple base stations, a wireless network is able to provide radio coverage to mobile stations over large geographic areas. The coverage area of a collection of neighboring base stations is commonly referred to as a location area. A location area is served by a mobile switching center (MSC), and a MSC may serve multiple location areas. The MSC is the network node that provides circuit-switched calling, mobility management, and various other services (e.g., telecommunications services, mobile services, and the like) to mobile subscribers. The MSC maintains subscriber data for the mobile devices that are currently located within the location areas served by the MSC. Mobile subscriber data is permanently maintained in a home location register (HLR) within the wireless network. When a mobile device is within the range of an MSC, the MSC acquires the mobile subscriber data from the HLR and maintains it in a visiting location register (VLR) associated with the MSC. The location area of the mobile station is also maintained in the VLR associated with the MSC, for use by the MSC to page the mobile device in the location area when a mobile termination (MT) call is intended for the mobile device. The MSC that is associated with the current location area of a mobile station may be referred to as a visiting mobile switching center (VMSC) relative to the mobile station. The MSC receiving an MT call that is intended for the mobile subscriber may be referred to as a Gateway MSC (GMSC) for the mobile device. A combination of the MSC and the VLR for the MSC also may be referred to as an MSC/VLR.
When a mobile device moves, the mobile device may move from a current (or old) cell to a new cell, where the old cell and new cell may be part of the same location area or different location areas. The mobile device determines whether it has roamed from an old location area into a new location area by comparing location area identifiers (LAIs) of the old cell and the new cell when the mobile device moves from the old cell to the new cell. When a mobile device moves or “roams” from an old location area into a new location area (e.g., when the mobile device determines that the LAI of the old cell and the LAI of the new cell are different), the mobile device informs the wireless network of the change in location areas by sending a location update request to the wireless network (which requests that a location update procedure be performed). When the new VMSC serving the new location of the mobile device is different than the old VMSC serving the old location of the mobile device, an inter-VLR location update is performed as part of the location update procedure.
During the inter-VLR location update, the new VMSC that receives the location update request from the mobile device transmits an update location message to the HLR of the mobile subscriber. The HLR, in response to receiving the update location message, forwards the subscriber data associated with the mobile subscriber to the new VMSC for temporary storage in the VLR of the new VMSC, updates its own records to indicate that the mobile device is now served by the new VMSC, and sends a message to the old VMSC to request that the old VMSC delete its own subscriber record for this mobile subscriber since the mobile device is no longer being served by the old VMSC. Once the location update procedure is complete, the mobile device stores the new LAI of the new location area and can continue to receive mobile services through the new VMSC of the new location area.
In a typical MT call scenario, an incoming MT call to the mobile device is first routed to the GMSC of the mobile device, e.g., to the GMSC of the Home Public Line Mobile Network (HPLMN) of the mobile device. The GMSC, upon receiving the incoming MT call, queries the HLR of the mobile subscriber to determine the VMSC on which the mobile station is currently registered. The HLR typically obtains routing information from the VMSC and returns it to the GMSC. The GMSC uses the routing information to route the call to the VMSC. The VMSC accesses its subscriber data for the mobile subscriber to determine the location area of the mobile device and pages the mobile device within that location area in order to set up a call connection between the caller and the mobile device of the mobile subscriber. However, if the MT call is received during the time that the mobile device is involved in an inter-VLR location update, the MT call may not be completed to the mobile device. For example, if the HLR has not yet been informed of the change in the VMSC of the mobile device when the GMSC queries the HLR for routing information, the HLR will return the routing information for the old VMSC to the GMSC and, thus, the GMSC will route the MT call to the old VMSC rather than the new VMSC. The old VMSC will then attempt to page the mobile device within the old location area of the old VMSC, however, since the mobile device is no longer in the old location area of the old VMSC, the mobile device will not be able to answer the page. One mechanism for dealing with this situation is Mobile Termination Roaming Retry (MTRR). A more recent mechanism for dealing with this situation, as well as other situations where the mobile device moves from an old MSC to a new MSC, is the Mobile Terminating Roaming Forwarding (MTRF) procedure.
MTRF is a procedure that enables delivery of an MT call to mobile device that moves from an old MSC/VLR to a new MSC/VLR during the delivery of the MT call (e.g., as described in sub-clauses 5.2.3 and 5.2.4 of Third Generation Partnership Project (3GPP) Technical Specification (TS) 23.018). For example, the MTRF procedure may be performed as a result of performing Circuit-Switched Fall Back (CSFB) when the mobile device moves from Long Term Evolution (LTE) coverage to a Global System for Mobile (GSM) EDGE Radio Access Network (GERAN)/Universal Terrestrial Radio Access Network (UTRAN) cell that is served by an MSC/VLR that is different than the MSC/VLR that initiated the SGs paging request (e.g., as described in sub-clause 7.5a of 3GPP TS 23.272). Similarly, for example, as discussed above, the MTRF procedure also may be used in at least some non-CSFB situations. Disadvantageously, however, use of the MTRF procedure to extend an MT call from the old MSC/VLR (the MSC/VLR which served the called mobile device before the delivery of the MT call/paging procedure) toward the new MSC/VLR (the MSC/VLR which serves the called mobile device after the paging procedure is complete) may result in a call loop between the old MSC/VLR and the new MSC/VLR under certain conditions.